1. Field of the Invention
The present invention relates to a video memory device.
2. Description of the Related Art
Video recording/reproducing apparatus such as video tape recorders are typically arranged so that, if special reproduction such as still image reproduction, stroboscopic reproduction or slow-motion image reproduction is to be performed utilizing field memories, switching signals for rotary heads or rotation control signals of the rotary heads are utilized to start writing and reading of the field memories. In the case of still image reproduction or stroboscopic reproduction, in order to correct skew corresponding to 0.5 H (H: horizontal period), the switching signal and the rotation control signal are utilized to drive a counter to generate a period signal of one vertical period .+-.0.5 H, and the period signal is employed to start writing and reading of memory. In this arrangement, one period of reading or writing of memory is made approximately equal to an integral multiple of one horizontal period, and writing and reading are performed in units of horizontal scanning periods, thereby preventing occurrence of skew of 0.5 H.
However, the aforesaid conventional arrangement has a number of problems. For example, if a video signal input to a memory includes jitters due to variations in the speed of rotation of the rotary head during recording and reproduction, a video signal written into the memory during each period is not always equal to an integral multiple of one horizontal scanning period. With regard to reading from the memory, the period of an output video signal is not always equal to an integral multiple of one horizontal period. For these reasons, if writing to the memory is halted or intermittently repeated while reading from the memory is repeated as in the case of still image reproduction, stroboscopic reproduction or slow-motion image reproduction, a skew may be formed at the gap between successive reading cycles. If such an output video signal is supplied to a television set, the image displayed on a screen is too curved to be easily identified.